Device Family: Cyclone® III, Cyclone® III LS, Cyclone® IV E, Cyclone® IV GX

Type: Answers

Area: Component

Do differential SSTL and HSTL inputs in Cyclone III and Cyclone IV series devices require a VREF input to reference?


Yes, usage of these I/O standards as inputs does also require a VREF input. This is because, in Cyclone® III and Cyclone IV series devices, these differential inputs are treated as two single-ended HSTL and SSTL inputs and only one of them is decoded. Hence a VREF is required to define the signal state.